The deep ocean is not a well-understood environment. It has been only 30 years since hydrothermal vents, and the zoo of bizarre creatures that inhabit them, were first discovered on the Pacific seafloor near the Galapagos Islands. Before that time, the consensus among scientists was that Earth’s ocean depths were dead zones.

Since then, however, hydrothermal vent systems around the world have been catalogued and studied. Submersible vehicles have done much of this exploration, some of them piloted by humans, others operated remotely. But studies of deep-ocean environments have been brief, episodic. They have allowed scientists to obtain snapshots of what goes on in there, but not to understand it dynamically.

What, for example, happens when a new hydrothermal vent first erupts on the seafloor? How does the water chemistry change? Which organisms appear first? How does the biological community develop over time?

The Deep-ESP project – ESP stands for Environmental Sample Processor – is designed to begin answering these questions, to study how deep-sea ecosystems respond over time to changes in environmental conditions. Developed by a group of scientists and engineers at the Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing, California, and funded in large part by NASA’s ASTEP (Astrobiology Science and Technology for Exploring Planets) program, Deep-ESP recently began a new round of field tests.

In these experiments, Deep-ESP will descend to sites as deep as 1800 meters (5900 feet) and, in its final test, will be left on the seafloor for a year, operating without human intervention, monitoring the environment for signs of sudden changes in temperature or water chemistry, then springing into action to study the resulting shifts in the biological community.

Deep-ESP has two major components: a core, responsible for performing sophisticated DNA and other biological analyses; and a deep-water-sampling unit, responsible for collecting ocean water, depressurizing it and passing it through the core.

Deep-ESP has been in development for several years, but it recently underwent a major upgrade. In its current configuration, the core remains unchanged, but the enclosure that houses it is completely new. The new enclosure is a shiny titanium sphere.

The earlier pressure housing was a long cylinder weighing about 950 pounds, but it was designed for use only to a depth of about 1000 meters. A cylindrical housing the same size, capable of withstanding the pressure at 1800 meters, would have required walls two inches thick, resulting in a device weighing nearly a ton.

In contrast, the new pressure housing, a titanium sphere some 40 inches in diameter, will allow the ESP to travel to depths up to 4000m, over 2 miles below the ocean surface where the pressure is 6000 pounds per square inch. Yet it weighs only 900 pounds, and “has three times the volume inside,” said Doug Pargett, the MBARI engineer who designed the sphere. The extra room can be used to mount custom analytical modules inside the sphere.

In late April and early May, the spherical model of the Deep-ESP took its first dip in the Pacific Ocean, at a site in Monterey Canyon, about 10 miles off the coast of central California, at a comparatively shallow depth of 650 meters.

In its new configuration, the instrument was designed to work as an “elevator,” deep-sea-research lingo for a device that descends and returns to the surface on its own. Attached to the bottom of the cage in which the sphere was mounted was a 600-pound steel bar, which made the ESP sink to the bottom. When its underwater operation was completed, the weight was dropped, and the sphere floated to the surface.

Actually, this elevator function, new to the spherical ESP, was part of the recent test. The earlier, cylindrical ESP was carried to the ocean floor and returned to the surface by MBARI’s ROV Ventana. Ventana did, however, play a role in testing the sphere, as well. The surface of the sphere contains a “wet-mate” connector, for making underwater network connections. Once the Deep-ESP reached the bottom, Ventana, tethered electronically to the ship via a long fiber-optic cable, was sent down to plug into the device. “Literally we plug into the machine and then we can talk to it just as if you had a hardwire Internet connection to it,” said MBARI’s Chris Scholin, principal investigator for the project. Engineers onboard the ship then feed the instrument instructions to perform various tasks.

Deep-ESP with the top half of its spherical enclosure removed, exposing the instrument core, where sample preparation and analysis is performed.
Credit: Henry Bortman

The deep-water sampling unit, also newly designed since the previous series of field tests, is capable of sucking in a maximum of 10 liters of water. In the recent maiden voyage it acquired only 2 liters. The sampling unit then depressurized the seawater, before passing it through the core. Surface-level pressure is maintained inside the sphere; if high-pressure deep-sea water were passed directly through the core, it would destroy the instrument.

The entire volume of collected water was passed into the core, through a filter and back out. The good stuff, the material the scientists are interested in, is what stayed behind on the filter. It’s a tiny amount. “Imagine a filter that’s discolored,” said Scholin. “We’re not talking like a big dome” of material, “it’s just sort of like the filter’s stained.” But that’s where all the biology is to be found. That material was then dissolved and homogenized, using various chemical reagents contained in bags of fluid within the core. The end result was about two milliliters of “this concentrated extract, this dirty dishwater,” said Scholin. “We started with two liters of liquid, and we end up with two milliliters,” he said, “about a thousand to one reduction.”

In the final step, this concentrate was fed to the DNA-analysis module of the core, which, after a series of additional biochemical reactions, produced an array of tiny fluorescing dots, each dot representing the presence of a particular organism in the sample. A digital camera mounted inside the core then took an image of the array and sent it up to computers on the surface.

There were no scientific discoveries on the April-May cruise, but then none were expected. Its purpose was merely to test out the end-to-end function of the system’s new components, all of which performed well.

Additional field tests are planned throughout the remainder of the year, some focused on ensuring that Deep-ESP can perform at depths up to 1800 meters, others focused on placing the device on the ocean floor for extended periods of time to validate its intended use as an instrument for long-term studies.